The present invention relates generally to the wheel of an extrusion blowmolding apparatus. Specifically, the present invention relates to an extrusion blow molding wheel having a disk comprising a plurality of distinct and separate segments.
Conventional extrusion blow molding apparatuses typically comprised a wheel mounted on a rotating shaft and having a plurality of molds positioned on the wheel about the shaft for rotating the plurality of molds past an extrusion die extruding a continuous parison. Each mold typically included two mold halves each comprising a mold cavity half therein so that when the mold halves were closed the mold defined a mold cavity corresponding to the configuration of the article to be molded, such as a container. Blow molding with such an extrusion blow molding apparatus entailed rotating the wheel to move each mold, seriatim, past the extrusion die with the mold halves in an open configuration and closing the mold halves of each mold around the parison to enclose the parison within the mold defined by the mold halves. The apparatus then inserted a blowing needle into the parison within the closed mold and introduced internal pressure to the parison, forcing it to inflate and conform to the configuration of the mold cavity. The molded object was then cooled and the mold opened to release the molded object from the mold.
The wheel of prior extrusion blow molding apparatuses was comprised of a hub mounted to the rotating shaft and a wheel disk secured to the hub and extending radially therefrom. The molds and mold operating mechanisms were secured to the wheel disk in a position to facilitate delivery of the molds to the extrusion die situated adjacent to the wheel. The wheel disk of prior extrusion blow molding apparatuses comprised only a single piece. In order to accurately align the molds secured to the disk, the single-piece disk was required to be machined nearly perfectly planar. Molds located on portions of the disk that were out of planar would be out of alignment with the remaining molds and, therefore, out of alignment with the extrusion die from which the mold would receive the parison. Misalignment of the parison within the mold caused uneven material distribution and side flashing in the resulting product blown therefrom as understood by those of ordinary skill in the art. For example, it has been found that extrusions blow molding apparatuses having single-piece disks of 100 inch or greater diameter typically experienced mold misalignment of 0.2 inches of more. Larger diameter disks magnified this misalignment.
Machining a large single-piece planar disk and overcoming issues such as spring-back after releasing machining clamps made manufacture of the single-piece disk difficult and expensive. Even when a single-piece disk was machined to be planar within acceptable tolerances, the large, single-piece nature of the disk made it difficult to transport and susceptible to damage during transport or assembly of the blow molding wheel. Severe damage to a portion of the single-piece disk necessitated replacement in its entirety. Additionally, it has been found that over time, single-piece disks tended to warp out of plane due to material relaxation and other factors as is recognized by one of ordinary skill in the art.
Accordingly, there is a need for an improved disk for extrusion blow molding apparatuses.
Accordingly, it is an object of the present invention to provide a wheel type extrusion blow molding machine having a disk that is easy to machine.
It is a further object of the invention to provide a wheel type extrusion blow molding machine having a disk that will substantially limit warpage.
It is another object of the invention to provide a wheel type extrusion blow molding machine having a disk that facilitates easy replacement of a severely damaged portion thereof.
It is yet another object of the invention to provide a wheel type extrusion blow molding machine having a disk that is comprised of a plurality of discrete and separate disk segments.
It is still further an object of the invention to provide a wheel type extrusion blow molding machine having a disk that is comprised of a plurality of discrete and separate disk segments and facilitates quick replacement of multiple molds by replacing one or more disk segments.
It is still another object of the invention to provide a wheel type extrusion blow molding machine having a disk that facilitates simple conversion from a disk of all like-configured molds to a disk carrying different molds having differing cavity configurations.
It is an additional object of the invention to provide a wheel type extrusion blow molding machine facilitating simple conversion from a disk of all like-configured molds to a disk carrying multiple mold cavity configurations by replacement of one or more segments of a segmented disk.
The above objects and other objects and features of the invention will be readily appreciated by one of ordinary skill in the art from the following detailed description of the preferred embodiment for carrying out the invention when taken in connection with the appended drawings.